The present invention generally relates to a liquid fuel combustion apparatus. Particularly, it is concerned with a wick assembly for combusting liquid fuel in such an apparatus.
2. Prior Art
A liquid fuel combustion apparatus of a type called "wick type" has hitherto been widely embodied as an oil stove, an oil burner and the like. Such an apparatus is usually designed to suction the liquid fuel by capillary action of the wick to lift it up to a top of the wick (i.e. a fuel vaporization part), the surface of which is exposed to an atmosphere of a combustion chamber in the apparatus, wherein the lifted fuel vaporizes to be burnt.
In such kind of the liquid fuel combustion apparatus, since its fuel vaporization part is always exposed to the high temperature atmosphere containing oxygen, a phenomenon, is likely to occur that a part of the fuel contained in the fuel vaporization part becomes a tar-like substance by being oxidized and polymerized to be piled up in the fuel vaporization part. Particularly, the formation and piling-up of said tar-like substance becomes remarkable, if the fuel contains a small amount of high boiling point fractions (for instance, machine oil, light or salad oil is mixed with kerosene), and if part of the fuel is deteriorated (for instance, the kerosene has been caused to contain oxides, peroxides or resinous components as a result of preserving the kerosene at a high temperature or being exposed to the direct daylight for a long period of time).
When the tar-like substance is piled up in the fuel vaporization part, the surface of that part or the capillary tube inside thereof is choked with the substance to obstruct the suctioning and vaporization of the fuel. Due to this phenomena, the vaporization of the fuel is abnormally decreased, to make an air to fuel ratio in the combustion chamber go wrong and to invite an inconvenience of generating a large amount of carbon dust or soot and noxious carbon monoxide. Moreover, this phenomenon of piling up the tar-like substance hinders a rapid rise-up of the temperature of the vaporization part and a rapid increase in the amount of vaporization at start-up time. Thus, it takes the apparatus a remarkably long period of time before reaching to a steady-state combustion and the phenomenon increases the undesirable generations of an objectionable odor, carbon dust and carbon monoxide due to an increased unstable transient-state combustion. In addition, the tar-like substance might stick to both of the wick and a metal part of the apparatus supporting the wick so as to cause them adhered or fixed together, to make the mechanical movement of the wick relative to the metal guiding pipe impossible, and to invite a dangerous state, wherein the turn-off of the apparatus by lowering the wick is made impossible due to such sticking.
As one of the methods for solving the above-mentioned problems, it has hitherto been known to be effective to increase the oil retaining ability of the wick top.
The method can be embodied by the following measure of;
(1) shortening the distance between the oil level and the top of the wick, PA1 (2) increasing the thickness of the top, and PA1 (3) employing a substance having an oil retaining ability as large as possible for the material of the main wick.
By taking the above-mentioned measure, the deterioration of the fuel vaporization part can be made hardly to occur even if the deteriorated kerosene or the kerosene containing a different kind of component is combusted. In such cases of increasing the oil content in the wick top, the tar-like component generates at the outside of the wick rather than the inside of the wick. As a result, the fuel-suctioning by the main wick is effectively prevented from being made insufficient.
However, when the tar-like substance is formed at the outside of the wick, a fire-spreading time at the start-up of the apparatus is made longer, because the formed tar-like substance makes the heat capacity of the wick top large. If the fire-spreading time is made longer in such way, the objectionable odor at the time of start-up increases and the carbon dust increases accordingly. Therefore, unless the fire-spreading time is shortened, the disadvantages cannot be overcome.